How Bad Is the US Drought?

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Nearly two-thirds of the continental United States is in the grip
of a drought, threatening agriculture, particularly corn, and
prompting the U.S. Department of Agriculture to declare a
disaster in more than 1,000 counties in 26 states — the largest
disaster in the history of the program.

A combination of factors, including the heat
wave that hit much of the country in June and earlier this
month, are blamed for the drought, which rivals the geographic
extent of the multiyear
droughts of the 1950s and the 1930s, a decade marked by the
historic Dust Bowl that devastated agriculture in the central
United States.

But while the USDA designated it to be the largest single
disaster of its history effective July 12, the drought itself is
not breaking records.

Large, but not unprecedented

In terms of the area affected, the current drought is parching a
similar amount of land as the multiyear droughts of the '50s and
'30s; however, it is not as severe or as long-lasting, said Mark
Svoboda, a climatologist with the U.S. National Drought
Mitigation Center at the University of Nebraska-Lincoln.

He refers to the current drought in the Midwest as a "flash
drought," because it arrived in a time frame of weeks to months,
relatively fast for a drought. The mild winter this year didn't
recharge soil moisture and the heat wave that arrived in late
June pushed some places over the cliff, Svoboda said.

This drought hit at a critical time for corn, with devastating
effects for the future harvest, Svoboda added.

Tom Vilsack, the USDA secretary, noted that the forecast for
other agricultural products, including soybeans and livestock,
had been hurt by the drought, and on July 11, announced a
streamlined disaster designation process intended to get aid to
affected areas more quickly, as well as other changes.

Heat and climate

While the unusual heat has contributed to the drought —
June ushered in the warmest 12-month period since
record-keeping began for the continental United States in 1895 —
it isn't the only cause. La Niña also played a part.

Part of a natural climate fluctuation,
a La Niña event is associated with cooler ocean surface
temperatures in the equatorial Pacific Ocean. La Niña affects
weather patterns around the world, and in the southern part of
the United States, it is associated with dry weather. Both this
year and last saw La Niña events, contributing to the current
drought.

The configuration of the jet stream, a band of high-altitude
westerly winds, also contributes, although its current position,
to the far north above the continent, is not uncommon for summer,
according to Mike Brewer, a physical scientist with the National
Oceanographic and Atmospheric Administration. The jet stream's
position keeps cooler air locked further north above it and lets
warmer, more southerly air dominateover
much of the United States.

Whether or not global warming is also a contributing factor is
more difficult to say.

"In global warming, we expect more extremes, more droughts, more
heavy precipitation. But we can't attribute this to global
warming," Brewer said. "This is inside the realm of what we have
seen before as evidenced by the '30s and '50s, when things were
even worse."

But he added: "If you look at global temperature, it is certainly
on the way up from what we can tell."